1. Field of the Invention
The present invention relates to a control apparatus for a marine propulsion unit, and more specifically, relates to a control apparatus for a marine propulsion unit that is preferably equipped with an engine control unit using a computer system in an outboard motor and is arranged to actuate a starter motor via the engine control unit with power from a battery on a hull to activate an engine.
2. Description of the Related Art
An outboard motor is generally disposed at the stern of a hull and a control compartment is provided in the front portion of the hull. An engine of the outboard motor is activated by remote operation of a switch panel that is provided in the control compartment. When the hull is large in size, the control compartment and the outboard motor are located remote from each other. Thus, it is difficult for an operator to recognize the engine sound, and the operator may keep actuating the starter motor even after the activation of the engine. In JP-A-Hei 6-213112, when an engine control unit that uses a computer system such as a microcomputer is installed in the outboard motor, the engine control unit controls actuation of the starter motor to activate the engine. According to this background art, because the computer system monitors the activation of the engine, it is possible to avoid continuous actuation of the starter motor after the engine start.
However, the computer system such as a microcomputer that is installed in the engine control unit is reset when supplied voltage thereto is lowered below a predetermined value. The term “reset” means that the computer system terminates the output in order to hold its own functions. Once the supplied voltage is restored to the predetermined value or greater, the reset is cancelled to recover the computer system. Generally, the outboard motor is not equipped with its own battery. Thus, the starter motor and the computer system for the engine control unit are actuated with power from the battery on the hull. However, when the hull is large in size, a cable that connects the battery and the outboard motor tends to be long. Therefore, even when a cable with low resistance per unit length is used, a voltage drop that is caused by resistance of the cable is unavoidable. Especially, the engine and its inertia force that acts on a watercraft are large in the large watercraft, and thus a large amount of power is required to actuate the starter motor. Consequently, there is a possibility that the supplied voltage from the battery may become lower than the reset voltage of the computer system. Once the supplied voltage becomes lower than the reset voltage of the computer system, the computer system is reset, and the starter motor stops. Thus, the engine cannot be activated.